Adam Lipski

Variations of the Specimen Temperature Depending on the Pattern of the Multiaxial Load – Preliminary Research

This paper provides the results of research on temperature changes of cylindrical specimens depending on the pattern of the multiaxial load. The research were made by using passive infrared thermography. It was found out that the average temperature value is significantly dependent on the plastic strain energy and that the temperature change amplitude depends on the nominal normal stress (except for torsion).

Determination of Fatigue Limit by Locati Methodusing S-N Curve Determined by Means of Thermographic Method

Selected results of experimental research showing possibilities to combined accelerated methods, i.e. thermographic determination of the fatigue curve and estimating the fatigue limit, were presented in this paper. The tests were performed using the reversed bending fatigue-testing machine with a rotational frequency of 77 Hz. The main item of the test station was the thermographic camera. Test specimens were made of C45 (1.0503) steel drawn bars. The full tests results were presented for the fatigue S-N curve (23 specimens at 10 load levels) and fatigue limit by the Staircase method (25 specimens) based on 107 cycles to failure was determination. The accelerated test for determining the slope of the S-N curve and the fatigue limit were made by a single specimen based on gradually increasing loading. Methods previously presented in the literature are based on the phenomenon of temperature stabilization during most of the fatigue process. The results presented in this work did not show the occurrence of such a phenomenon. For that reason, the new approach to the determination of the slope of S-N curve was proposed. Combined application of both experimental methods, Locati and thermographic, with a new approach to the determination of this slope might allow one to develop automatic equipment for the accelerated determination of the fatigue limit which would contribute to significant reduction of the test costs and time, thus increasing availability of such tests.

Impact of the Strain Rate during Tension Test on 46Cr1 Steel Temperature Change

The aim of this paper was to assess influence of the strain rate on the specimen temperature change during monotonic tensile test. Based on the assessment of this change under variable strain rate, it was determined the level of internal specimen energy change. The assessment to extent to which the adiabatic testing conditions were maintained was made based on this results.

Rapid Determination of the S-N Curve for Steel by means of the Thermographic Method

The paper presents a thermographic method of accelerated determination of the S-N curve. In the presented method, the S-N curve was developed based on energy-related parameter with the assumption of its dependency on the stress amplitude. The tests made on C45 steel and X5CrNi18-10 steel under reversed bending revealed that the S-N curve obtained by accelerated thermographic method fits inside the 95% confidence interval for the S-N curve obtained from the full test.

Use of Thermography for the Analysis of Strength Properties of Mini-Specimens

This paper presents sample applications of passive infrared thermography for research on temperature changes of mini-specimens resulting from monotonously increasing or cyclically variable mechanical load. The MFS system developed in the Department of Machine Design at the University of Technology and Life Sciences in Bydgoszcz (Poland) and designed for testing mechanical properties of microelements were used for tests. The MFS system ensures nanometric measurement accuracy of many static and fatigue-related material properties, including, i.a., static tension curves, cyclic strain curves, fatigue life curves as a function of force, stress and strain. Measurements of the mini-specimens temperature were performed using thermographic camera equipped with microscope lens. The tests have shown that research on the passive infrared thermography may be successfully applied for determining strength properties of materials in micro scale. The used research instrumentation is characterized by sufficient sensitivity and resolution (camera with the microscope lens), while the MFS system ensures accurate load and position control.

Plastic strain energy of CuZn37 brass in low-cycle multiaxial fatigue regime

This paper presents the results of a plastic strain energy calculations for the CuZn37 brass under multiaxial fatigue loading. Fatigue tests were performed on the hollow specimens subjected to fully reversed tension-compression, torsion, proportional loading, 90° out-of-phase non-proportional loading and two another non-proportional loadings with frequency differences. All test were strain-controlled. Calculations of a strain energy were based on midlife strain hysteresis loops data and Ramberg-Osgood equation constants. Some tests are observed by thermographic camera. The plastic strain energy was also determined on the base of the specimen surface temperature. All results were compared and discussed.

Steady-state temperature determination on the base of hysteresis loop energy for CuZn37 brass

This paper presents the verification of the relationship between the temperature and the hysteresis loop energy for the CuZn37 brass under multiaxial fatigue loading. Fatigue tests were performed on the hollow specimens subjected to fully reversed tension-compression, torsion, proportional loading, 90° out-of-phase non-proportional loading and two another non-proportional loadings with frequency differences. All test were strain-controlled. Calculations of a plastic strain energy were based on midlife strain hysteresis loops data. The calculated specimen temperatures were compared with temperatures observed by thermographic camera.

Proposition of Low-Cycle Fatigue Test Termination Criterion Based on Specimen Temperature Change

This paper presents proposition of the low-cycle fatigue test termination criterion based on specimen temperature change. The tests were performed using specimens made of G-X12CrMoVNbN9-1 (GP91) martensitic cast steel under axial tension-compression conditions with strain controlled at the total strain amplitude levels amounting to εac = 0.25%, 0.5% and 0.6%. Very good compliance of the proposed criterion with the criterion used so far was obtained. The discrepancy for the tested material has not exceeded 2% in the εac stress range not exceeding 0.5%.

Accelerated Determination of the Fatigue Limit and the S-N Curve by Means of the Thermographic Method for C45 Steel

The paper presents a new thermographic method that enables simultaneous accelerated determination of the fatigue limit and the S-N curve. In the presented method, the fatigue limit was determined assuming a constant rate of temperature rise occurring in the second phase of a specimen fatigue life. The S-N curve was developed based on energy-related parameter with the assumption of its dependency on the stress amplitude. The tests made on C45 steel under reversed bending revealed that the fatigue limit value obtained from accelerated thermographic tests as compared to the value obtained using Staircase method differs by 10.0% maximum.The S-N curve obtained by accelerated thermographic method fits inside 95% confidence interval for the S-N curve obtained from the full test.

Temperature Changes Induced by the Portevin-Le Châtelier (PLC) Effect during Tensile Test Based on the Example of CuZn37 Brass

This paper presents results of research on PLC effect in CuZn37 brass. A thermographic camera was applied in the tests for determining surface temperature distributions of the tested specimens during tension. Spatial-temporal diagrams were prepared on the basis of those distributions. The tests were performed at two strain rates. No significant difference in the tension curve course depending on the above rate was found. Significant difference was observedas regards the course of specimen temperature changes. Increased frequency of the permanent strain wave propagating along the specimen centerline was observed together with the increase of the wave propagation speed for the higher strain rate. Simultaneous initiation of two propagating waves in opposite directions was observed in case of the higher strain rate.